There is to me much that reflects both dark and light aspects of the Moon in the Marseille Luna. Firstly, if as I believe this image does reflect the appearance of an eclipse [which as an image is perhaps more apparent in some decks than others], then we have in one image a symbol of both night and day; an aspect also reflected in their being a dark and a light dog, the moon hounds thus reflecting the fact that the Moon appears both during the night and during the day. The towers too can be seen as symbols of east and west which combines with what has already said in previous posts as to how we may see in this card the transience of temporal time, and thus not only of the transience of our sufferings but our joys also: as it is said, "This too will pass". So the Moon has 'swallowed' the Sun but it will emerge again 'reborn' from the other side of the moon in its passing. But not only do we have the rebirth of the Sun, a solar eclipse can only occur during the three day period of the dark of the Moon, from whence the crone re-emerges as the maiden. So both Sun and Moon reflect the concept of rebirth and renewal. In the heavenly moon, the moon hounds of terra firma and the moon water creature we may also have a reference to the triple aspect of the moon having rule over the celestial world, the terrestrial and the underworld [artemis/diana; demeter and proserpine/hecate?].
Yes the card speaks of grief, of sorrows and lamentation; but that does not mean our vision should be limited by the confines of our temporal existence. The card to me reminds us of the continuity, the cycle of life; that death is not the opposite of life. For life, being eternal, is singular not dual and thus has no opposite. Yes there are sorrows and grief, but when you look down into the grave don't let your gaze remain fixated there as a profane worshipper of death, look up unto the vast eternity of heaven and remember, this too will pass.
Kwaw